The present invention provides an a.c. elevator having a commercial power source, an inverter operable with the power from the commercial power source for generating a.c. power, and an electric motor to be driven with the a.c. power generated by the inverter. A power source device for the a.c. elevator comprises a rechargeable/dischargeable battery, a charge/discharge circuit for charging and discharging the battery, and a control circuit for controlling the voltage to be input to the inverter by according to a predetermined voltage command serving as a target value controlling the operation of the charge/discharge circuit, the battery being chargeable with regenerative power from the electric motor, the battery being operable to generate power and supply the power to the inverter.
As shown in FIG. 16, elevators generally have a well bucket construction which comprises a rope 83 wound on a hoist 82 and provided with an elevator car 8 connected to one end thereof and a counterweight 81 connected to the other end thereof. The weight of the counterweight is so adjusted as to be in balance with a load corresponding to 40 to 50% of the rated movable load.
With progress in power electronics devices and techniques for controlling these devices in recent years, inverter drive systems are placed into use which comprise an inverter 3 for supplying voltage-variable frequency-variable a.c. power to an induction motor of the hoist 82 as illustrated for speed control to lift and lower the elevator car 8.
When the car as fully occupied is lifted or when the car is lowered in an empty state with the elevators of the inverter drive type, there is a need to increase potential energy, so that the increase of energy is supplied from the power source 1 to the induction motor through an converter 2 and the inverter 3. Such an operating mode is termed a xe2x80x9cload lifting operation.xe2x80x9d Conversely when the car is lifted in an empty state or is lowered as filled with passengers, the potential energy is to be decreased, and the decrease of potential energy is converted by the induction motor to electric energy (electric power) and returned to the inverter 3. This operating mode is termed a xe2x80x9cload lowering operation,xe2x80x9d and the power to be returned to the inverter 3 is termed xe2x80x9cregenerative power.xe2x80x9d Unless this regenerative power is treated by some method, the input voltage of the inverter will increase to break control elements.
Accordingly already known are a method of returning the regenerative power to the power source using a converter comprising transistors and adapted to regenerate the power source, and a method of dissipating into air the regenerative power as converted to heat by resistance. The former method is used chiefly for high-speed elevators in high-rise buildings, while the latter method is used for medium- to low-speed elevators in medium to low buildings.
The converter for use in the former method exhibits a high conversion efficiency, affords a power factor of nearly 1, is therefore very excellent, but has the drawback of necessitating an expensive apparatus. On the other hand, the latter method is easy to control and inexpensive in apparatus, but has the problem of being low in energy utilizing efficiency since the regenerative power is released as heat.
For use with electric motors for driving elevators, a power source device has been proposed which comprises a battery connected in parallel with a d.c. power supply unit of constant voltage and to be charged with regenerative power when the elevator motor is decelerated, such that the battery chiefly supplies current to the motor when the motor is accelerated [JP-B No. 53-4839(1978)]. With the proposed power source device, however, there must be a specific corresponding relationship between the voltage regulation characteristics of the rectifying circuit for converting the a.c. output of the power source to direct current and the voltage regulation characteristics of the battery, whereas it is difficult to design a rectifying circuit and battery which will fulfill such a corresponding relationship. Thus the proposed device has the problem of being difficult to realize.
Accordingly, an object of the present invention is to provide a power source device for a.c. elevators which achieves a high energy utilization efficiency and which is nevertheless easy to realize.
The present invention provides an a.c. elevator having a commercial power source, an inverter operable with the power from the commercial power source for generating a.c. power, and an electric motor to be driven with the a.c. power generated by the inverter. A power source device for the a.c. elevator comprises a rechargeable battery, a charge/discharge circuit for charging and discharging the battery, and a control circuit for controlling the voltage to be input to the inverter by controlling the operation of the charge/discharge circuit, the battery being chargeable with regenerative power from the electric motor, the battery being operable to generate power and supply the power to the inverter.
The predetermined voltage command has a value corresponding to a constant voltage higher than full-wave rectified voltage of the commercial power source. The charge/discharge circuit has a charge control element for closing a charge circuit and a discharge control element for closing a discharge circuit, and the charge control element and the discharge control element are on/off-controlled by the control circuit.
The control circuit alternately turns on the charge control element and the discharge control element to alternately charge and discharge the battery. According to the charged state of the battery or the operating state of the elevator, the control circuit alters the on period of the charge control element and the on period of the discharge control element relative to each other to determine the priority of charging by the charge circuit or discharging by the discharge circuit.
Consequently, the input voltage of the inverter is controlled to a constant level. For example during the load lowering operation, regenerative power supplied from the motor via the inverter is delivered to the battery for charging, while during the load lifting operation, the power generated by the battery is supplied to the motor via the inverter.
The control circuit comprises discharge restricting means for restricting the discharging of the battery and charge restricting means for restricting the charging of the battery. The charge restricting means of the control circuit prevents charging of the battery upon the charged state of the battery exceeding about 80% of the rated capacity thereof to thereby prevent overcharging. The discharge restricting means of the control circuit prevents discharging of the battery upon the charged state of the battery dropping below about 30% of the rated capacity thereof to thereby prevent overdischarging.
The charge restricting means and the discharge restricting means of the control circuit comprises a limiter circuit for imposing limitation on the deviation of the input voltage of the inverter from the voltage command thereof. The charge-side limiter value of the limiter circuit is set to zero upon the charged state of the battery exceeding about 80% of the rated capacity thereof. The discharge-side limiter value of the limiter circuit is set to zero upon the charged state of the battery dropping below about 30% of the rated capacity thereof.
The control circuit comprises a discharge preventing means for preventing discharging of the battery under a predetermined condition. The control circuit comprises a charge preventing means for preventing charging of the battery under a predetermined condition.
The control circuit further comprises means for presetting capacity measuring means for measuring the capacity of the battery, upon completion of charging of the battery, and means for resetting capacity measuring means for measuring the capacity of the battery, upon completion of discharging of the battery, whereby an accumulated error of the capacity measuring means is eliminated.
The control circuit comprises means for changing over discharging from the battery to constant-current control and changing over charging of the battery to constant-current control, and means for detecting the internal resistance of the battery based on the terminal voltage of the battery during discharging and the terminal voltage of the battery during charging. Accordingly, the life of the battery can be judged from the variation of the internal resistance.
The power source device of the present invention comprises an output contact provided between an input terminal of the inverter and the control circuit and controllable for opening and closing, a comparator for comparing the input voltage of the inverter with the terminal voltage of the battery, and control means for closing the output contact upon said input voltage exceeding said terminal voltage, whereby rush current is suppressed when the output contact is closed.